In recent years, to reduce power consumption, various apparatuses have been provided with a power-saving function. For example, there are storage apparatuses that have a function of setting hard disk drives (HDDs) in a power-saving mode for a predetermined period. For example, when an HDD is set in a power-saving mode, rotation of its magnetic disks is stopped. In this way, the power consumption of the storage apparatus can be reduced.
An information processing apparatus has been proposed as an example of power-saving technology. When setting an HDD in a power-saving mode, depending on the status or purpose of use, the information processing apparatus causes the HDD to forward predetermined data to a fixed-data area allocated in a memory that is not set in the power-saving mode.
See, for example, Japanese Laid-open Patent Publication No. 2000-250716
Among these storage apparatuses, each of which includes a plurality of storage devices and has a function of holding part of the data stored in these storage devices in a cache, there are storage apparatuses, each of which has a function of staging data from a storage device to a cache asynchronously with access to the data by a host apparatus. This staging processing is a kind of processing for prefetching data to a cache. If such storage apparatus as described above is provided with a function of setting a storage device in a power-saving mode for a predetermined period, the following problem could arise.
While a certain storage device is in a power-saving mode, if prefetching data stored in the storage device to a cache is performed, the power-saving mode of the storage device is canceled. In many cases, a period in which a storage device is set in a power-saving mode is a period in which the data stored in the storage device is less likely to be accessed by a host apparatus. Thus, even if the data is prefetched to a cache, the prefetched data is less likely to be accessed by the host apparatus immediately. In this sense, even if the data is prefetched in this period, the access response performance is improved very little. Therefore, if execution of a data prefetch operation is requested on a storage device in a power-saving mode, although the storage device is in a period in which the power-saving mode does not probably need to be canceled, the power-saving mode is canceled. Namely, there is a problem that unnecessary power could be consumed.